Subtrochanteric femur fractures

Introduction

Subtrochanteric fractures are fractures that occur in a zone extending from the lesser trochanter to 5cm distal to the lesser trochanter, however extension into the intertrochanteric region is common. These fractures are more difficult to treat as compared to intertrochanteric fractures due to the powerful muscle forces acting on the fragments as well as the tremendous stress that is normally placed through this region. When seen in young patients, they are due to high-energy trauma or pathologic fracture with 10% of high-energy fractures due to gun shot wounds. In the elderly, they are often low energy injuries involving osteoporotic bone. Pathologic fractures account for 17-35% of all subtrochanteric fractures¹. Fracture may also occur at the site of screw placement for a previous femoral neck fracture if the inferior screw is placed too low (below the lesser trochanter), as this creates a cortical defect and stress riser.

Anatomy

Subtrochanteric fractures are fractures that occur in a zone extending from the lesser trochanter to 5cm distal to the lesser trochanter. The medial and posteromedial cortices of the subtrochanteric femur experience the highest compressive stresses in the body. The lateral cortex is under a high degree of tensile stress. These fractures occur at the cortico-cancellous junction. The high composition of cortical bone and subsequently the decreased vascularity impairs the capacity for healing of these fractures when compared to the abundant cancellous bone of the intertrochanteric region of the hip.

The proximal fragment is usually flexed and externally rotated by the pull of the iliopsoas and short external rotators, and abducted by the pull of the gluteus medius and minimus. The distal fragment is adducted and shortened by the pull of the adductors leading to a varus and procurvatum fracture alignment. These factors should be considered when attempting reduction.

Classification

Fielding Classification - This is an anatomic classification based on location of the fracture and is rarely used
Type I - at level of lesser trochanter
Type II - <2.5 cm below lesser trochanter
Type III - 2.5-5cm below lesser trochanter

Russell-Taylor Classification - This classification is based on integrity of the piriformis fossa. It was designed to guide treatment of intramedullary nails using a piriformis fossa starting point. This system may not be as important as it used to be, due to changes in entry point techniques and improved implant designs¹.
Type I - intact piriformis fossa
A - lesser trochanter attached to proximal fragment
B - lesser trochanter detached from proximal fragment
Type II - fracture extends into piriformis fossa
A - stable posterior-medial buttress
B - comminution of lesser trochanter

Orthopaedic Trauma Association Classification - Based on degree of comminution and mainly used for research purposes.

Presentation

Patients typically present in significant pain unable to ambulate with deformity of the proximal thigh. High energy mechanisms should receive a full trauma evaluation and careful inspection for open fracture. A detailed neurovascular exam of the extremity should be performed. Due to the size of the thigh compartment, hypovolemic shock is possible secondary to this fracture.

Subtrochanteric Fractures and Long-Term Alendronate Use

A relationship between long-term Alendronate use and subtrochanteric fractures has been established and is hypothesized to result from long-term suppression of bone remodeling. A retrospective case-control study of postmenopausal women presenting with low-energy femoral fractures reported bisphosphonate use in 15/41 subtrochanteric/shaft fractures vs. 9/82 age-, race-, and BMI-matched femoral neck and intertrochanteric fractures (odds ratio = 4.44, 95%CI = 1.77-11.35; p = 0.002). A common radiographic pattern consisting of a simple oblique fracture with cortical thickening and beaking of the cortex on one side was highly associated with bisphosphonate use. Patients with this fracture pattern had an average duration of alendronate use of 7.3 years, vs. 2.8 years for those without the pattern
. Up to 76% of these patients may have prodromal pain
. Patients with low-energy fractures who have been on long-term bisphosphonate therapy should have imaging of the contralateral femur. Prophylactic fixation should be considered if a contralateral stress fracture is found
. Consideration should also be given to discontinuing alendronate, in consultation with an endocrinologist
.

Diagnosis

For all hip fractures, an AP pelvis, internal rotation AP and cross-table lateral of the affected hip should be obtained. An MRI may also be required for pathologic fractures to evaluate the proximal femur for soft tissue extension of an underlying bone tumor. It is helpful to obtain a contralateral femur x-ray taken with a radio-opaque ruler or scanogram for patients with highly comminuted fractures as a means to measure the native femur length so that it may be reproduced during ORIF of the affected extremity. Patients with low-energy fractures who have been on long-term bisphosphonate therapy should have contralateral femur imaging to rule out impending fractures.

Treatment

Initially, the limb should be stabilized with Hare traction, Buck's traction or skeletal traction. If there will likely be a delay in surgical stabilization, femoral or tibial skeletal traction should likely be employed.

Nonoperative treatment in 90-90 skeletal traction followed by hip spica casting should only be employed in those whom surgery is deemed very high risk. 90-90 traction attempts to counteract the deforming muscular forces. Traction usually is required for 12-16 weeks.

Surgical stabilization is the standard of care. The treatment option include:

Intramedullary nail fixation is the preferred treatment. In general, intramedullary devices have been found to be almost twice as strong as extramedullary implants. First generation interlocking nails (centromedullary) are indicated when both trochanters are intact as the oblique locking screw is able to obtain adequate purchase. Second generation interlocking nails with a locking screw that extends into the femoral neck (cephalomedullary) offer more stable fixation and are indicated when the lesser trochanter is displaced or comminuted. Advantages of intramedullary fixation include 1) Potential for closed treatment with preservation of fracture hematoma and blood supply to fracture fragments, 2) Decreased the moment arm on the implant compared to a lateral plate and thus decreases the tensile stress on the implant, 3) Reaming the canal in preparation of the implant provides internal bone graft, 4) intramedullary implants have been found to be twice as strong as traditional extramedullary implants. Disadvantages include 1) the implant cannot be used to help facilitate reduction and the fracture site may need to be opened to affect a reduction and guide pin insertion, thus lessening benefits of closed intramedullary fixation. It is nonetheless critical to achieve reduction and to maintain this reduction (using instruments, an incision or both as needed) while the nail is being placed. Failure to do so will result in varus displacement during implantation. Obtainment of proper nail starting point can be eased by lateral/lazy lateral patient positioning or the use of a trochanteric starting nail. If a trochanteric nail is chosen, it is imperative that a very medial starting point is chosen, again to avoid varus deformity. Russell et al have reported decreased rates of malalignment using the Minimally Invasive Nail Insertion Technique (MINIT)
.

Ninety-five degree fixed-angle devices
Historically this was the most common device used for operative fixation. This is a fixed angle construct that provides rigid fixation. Advantages include 1) Offers a treatment option for fractures with comminution of the trochanters that may make intramedullary implant insertion difficult, 2) Provides for multiple points of proximal fixation. Disadvantages include 1) Technically very demanding, 2) Extensive soft-tissue dissection, 3) High risk of implant failure due to tremendous stress applied to the plate laterally.

Sliding hip screw
This device is indicated only for very proximal fractures. The sliding of the screw allows medialization of the distal fragment, which reduces bending moment on fracture and implant. The sliding mechanism must cross the fracture site to lessen the risk of implant failure and the posteromedial cortex must be reconstructed to decrease the stress on the device.

Post-Operative Care

Rehab: Weight bearing is guided by fracture pattern. Protected weight bearing can be started early in fractures with posteromedial bony contact¹. Most patients should not fully bear weight for the first 6-8 weeks.

Complications

Nonunion. Incidence of 0-8%
. Presents with continued inability to bear weight at 4-6 months and continued pain. Varus malreduction is an important predictor of nonunion accompanied by implant failure.

Malunion:

Coxa varus: Caused by uncorrected abduction deformity, nail entry point that is too lateral, and migration of hardware proximally in the femoral head and neck.

Shortening: Due to uncorrected shortening intraoperatively and premature dynamization.

Rotational deformity: Do to uncorrected external rotation of proximal fragment. This can be assessed intraoperatively with visualization of the lesser trochanter.

Fixation failure: Most common in osteoporotic bone. Screw cutout in the femoral head; backing out of locking screws.

Failure of implant: Excessive motion at fracture site leads to implant fatigue.

Infection:

Red Flags and controversies

Plate vs. intramedullary fixation.

Role of locked plating and navigation.

Fracture may also occur at the site of screw placement for a femoral neck fracture if the inferior screw is placed too low as this creates a cortical defect and stress riser.

Outcomes

Currently, most subtrochanteric fractures in which the piriformis fossa or greater trochanter are intact can be successfully treated with a cephalomedullary device. Care must be taken to avoid varus during placement of the device. Comminuted subtrochanteric fractures may be treated with a long intramedullary device or a fixed angled plate. Sliding hip screws should generally be avoided as they have higher failure rates.

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